The overall goal of this proposal is to build upon and expand our unique clinical and specimen resource of hereditary non-polyposis colorectal cancer (HNPCC) patients to further elucidate genetic and epigenetic factors associated with increased risk for HNPCC. Epidemiologic data will be obtained on 400 subjects carrying germline mutations in either the hMSH2 or hMLH1 gene. It is hypothesized that genes playing minor roles in risk of cancer, modifier genes, are important in predicting risk of colorectal cancer in HNPCC. Polymorphisms in cell cycle genes such as cyclin D1, p53, and p21, will be studied to determine if they influence age of onset in HNPCC. Environmental factors, particularly those involving the folate pathway and heterocyclic amines intake will be studied to determine if they are associated with risk of HNPCC. Polymorphisms in metabolic genes such as N- Acetyltransferase 1 (NAT1), N-Acetyltransferase 2 (NAT2), Glutathione S-transferase M1 (GSTM1), Glutathione S-transferase T1 (GSTT1), will be studied to determine if they influence age of onset of HNPCC, and then to determine if any of the four genes, in combination with dietary intake data (with emphasis on heterocyclic amines) influence age of onset in HNPCC. A polymorphism of the Methylene tetrahydrofolate reductase (MTHFR) gene at codon 677 will be studied to determine if it influences age of onset of HNPCC, and then to determine in combination with dietary intake data (with emphasis on folate) if it influence age of onset of HNPCC. Models will be developed to predict i) the risk that an individual with MMR mutation will develop specific cancers and ii) the probability that a CRC patient will have a MMR mutation given the age at onset, MSI status (where known), and family history. For the first type of model, we will use the newly developed kin-cohort approach. To predict the probability that an individual is a mutation carrier, we will apply logistic regression and Classification and Regression Trees (CART). This will be the first large systematic study on the roles of modifier genes in HNPCC. The proposed studies will provide important information regarding underlying genetic and epigenetic factors involved in colorectal carcinogenesis in HNPCC and has the potential to provide novel insights into the molecular pathways that might influence this process.